Sound translating device



May 6, 1941. A. E. wooDRur-'F Erm.

' souND TRANSLATING DEVICE Filedmay 24, 1938` F'IG.7

FIG. a

F I G 9 FIG IO INVENTORS; ALBERT E. WOODRUFF ALBERT F. HORLACHER @waag/14M? 54a 4a I 5 4 a I Fl G. 1| yl mi/ M ATTORNEY ying signal voltage.`

enema May 6,1941

SOUND TnANsLA'rING DEVICE Albert Earl -Woodrufh Oak Park, and Albert lFredex-ck Horlacher, Chicago, Ill'., assignors to Associated Electric Laboratories, Inc.,` Chicago, Ill., a corporation of Delaware Application May 24, 1938, Serial N0. 209,802

11 claims. (01.179-,1191- v scribed comprising a-fleld'structure anda wind- 'Ihe present invention. relates to sound translating devices and more particularly to a sound translating device of the magnetic or sound powered type.

In a sound translating device of this type ar magnetic field structure is provided which ccnventionally comprises a bar magnet having field members formed of magnetic material arranged on the opposite ends thereof. Also, the eld members are provided with outwardly extending body portions, each, carrying two pole pieces spaced from each other and constituting two sets, the pole pieces of each of the sets being directed toward each other, and the pole faces of each set being arranged in spaced-apart relation in order to receive therebetween the opposite ends of a pivotally mounted armature formed of magnetic material. One end of the pivotally mounted armature is connected to a diaphragm and a winding or Voice coil carried by a winding spool is electromagnetically coupled to the armature.

In the case of a transmitter of -this type, the vibrations of the diaphragm produced bythe sound to be transmitted causes the ends of the armature to vibrate between the pole faces of the sets of pole pieces, thereby to generate a correspond- In the case of a receiver of this type, the signal current passing through the voice coil causes the ends of the armature to vibrate between the pole faces of the sets of pole pieces, thereby to reproduce at the diaphragm a corresponding sound. In prior sound translating devices of this type it has been possible to produce only two or three bars of pressure in the receiver with an input pressure of twenty bars in the transmitter, thereby restricting the use of this type of equipment to substations spaced apart only short distances. Furthermore, prior sound translating devices of this type embody field structures which are productive of strong stray magnetic elds.

Accordingly, it is an object of the present invention to provide an improved sound translating device of the type described which is of extremely simple and rugged construction, which is compact and economical to manufacture, and which is eiiicient in operation'. y

Another object of the invention is to provide an improved sound translating device of the type described, having embodied thereinv a field structure' which is so constructed and arranged that the production of stray magneticelds is mini- `mized.

Another Iobject of the invention is to provide 4 in a sound translating device of the type de'- ing spool, an improved arrangement for securing the eld structure in assembled-relation and for retaining the Winding spool in place.

A .further object of the invention is to provide in a sound translating device of the type described comprisinga field structure and securing and `spacing elements for retaining the field structure inassembled relation, an improved arrangement for compensating for the difference in the thermal coeiiicients of expansion of the securing and the spacing elements.

In general, the objects-as set forth 'above are attained in accordance with the present invention by providing in a sound translating device of the character noted, a fleld structure comprising` a. bar magnet, and field members formed of magnetic material arranged on the opposite ends of the bar magnet, the field members having recesses therein' receiving and surrounding the extreme outer ends of .the bar magnet, thereby to minimize uxleakage between the ends of the bar magnet.

Alsothe field members have outwardly extending` body portions, each carrying two pole pieces spaced from each other and constituting two sets, the pole pieces of each of the sets being directed toward each other and the pole faces of each set being arranged in spacedapart relation in order to receive therebetween body portions, each provided with two pole pieces spaced from each other and constituting two sets, the two pole pieces provided on each member being formed integrally from the stock of the member, the pole pieces of each of the sets being directed toward each other, and the pole faces of each set being arranged in spaced-apart relation in order to receive therebetween the opposite ends of a pivotally mounted armature formed of magnetic material.

In accordance with another feature ofl the invention a winding spool is provided with 'an armature formed of magnetic material pivotally mounted thereon, whereby .the Winding spool and armature constitute an assembly which is retained in place by securing and spacing elements arranged between-.the body portions of the field members of the field structure. In accordance with -.a further feature or the invention thereinterposed betwjeen one of the field members of the field structure and each oi' the spacing elements for compensating for the difference in the thermal coeicients of expansion of the securing and the spacing elements, whereby the adjustments of the elements of the sound translating device are not injuriously affected by ambient temperature variations. A

In accordance with a further feature of the invention the'bar magnet has a maximum energy greater than 1.2 x 10.6 ergs per c. c. and a coercive force greater than 400 Oersteds; the pole pieces have an A. C. permeability of the order of 600 to 800; and the armature has an A. C. permeability of the order of 500 to 1500.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with 'the accompanying drawing, in which Figure 1 is a sectional view of a sound translating device in the form of a telephone transmitter of the magnetic or`sound powered type embodying the present invention; Fig. 2 is a plan view, partly in section, of the sound translating device of Fig. 1; Fig. 3 is a side elevational view of the sound translating device;

Fig. 4 is a perspective view of an element of the field structure embodied in the sound translating device; Fig. 5 is a perspective view of a portionof a winding spool and armature assembly embodied in the sound translating device; Fig. 6 is a sectional view of the complete assembly taken along the line 5--6 of Fig. 5; Fig. 7 is a. plan view of a spacing element embodied in the sound translating device; Fig. 8 is a side elevational view of the spacing element of Fig. 7; Fig. 9 is a plan view of one of the eld members of a modified form of the field structure of the sound translating device of Fig. 1; Fig. 10 is a side elevational view of the field member of Fig. 9; Fig. 11 is a side elevational view of a resilient washer forming a part of an arrangement for securing the field members of the field structure in spaced-apart relation and for retaining the winding spool and armature assembly in place; and Fig. 12 is a plan view of the resilient washer of Fig. 11.

Referring now more particularly to Figs. 1 to 4, inclusive, of the drawing there is illustrated a sound translating device in the form of a telephone transmitter of the magnetic or sound powered type embodying the features of the present invention and comprising a field structure 20 and a winding spool and armature assembly 2|. The field structure 20 includes a permarient bar magnet 22 having a maximum energy greater than 1.2X 106 ergs per c. c. and a coercive force greater than 400 Oersteds, and two similar field members 23a and 23h formed of magneti'c material having an A. C. permeability of the order of S to 800 and arranged on the opposite ends of the bar magnet, the iield members 23a and 23b being arranged on the north and south poles, respectively, of the bar magnet 22. Preferably the bar magnet 22 is formed of an alloy comprising to 40% nickel, 'l to 20% aluminum, 0.5 to 30% cobalt and the remainder iron, such, for example, as the alloy known as Alnico;A

A while the field members 23B and- 23b are formed of an alloy comprising approximately 45% nickel and 55% iron, such, for'example, as the alloy known as Allegheny Electric Metal. Themembers 23 and 23b are of similar construction, each including outside and inside elements 24 and 25, respectively, formed of fiat stock and secured together in facing-engagement. The inside element 25 is seated in a recess 24a provided in the inner surface of the outside element 24, the elements 24 and 25 being secured together by rivets or the like extending therethrough. The inside element 25 is provided with an aperture 25 therethrough which is arranged in alignment with a solidportion of the outside element 24 secured thereto, thereby providing a recess in the eld member comprising the outside and inside elements 24 `and 25. The recess in the members 23 and 23b receive and surround the opposite and extreme outer ends of the bar magnet A22, thereby'to minimize flux-leakage between the portions of the bar magnet 22 adjacent the extreme outer ends thereof and the consequent production of stray magnetic fields.

Also, the bar magnet `22 is provided with a longitudinally extending recess 26 therein which is arranged in alignment with openings 21 and 28 formed in the members 23B and 23",v respectively, and adapted to receive Ya stud or the like for securing the eld members 23a and 23b to the bar magnet 22. Also, each of the elements 24 and 25 is provided with an extended body portion having a pole piece formed integrally therewith, the inside elements of the field members 23 and 23b being provided with pole pieces 29 and 30, respectively, and the outside elements of the eld ,members 23 and 23b being provided with pole pieces 3| and 32, respectively. The pole pieces 29, 30 and 3|, 32 constitute sets spaced from eachother, the adjacent pole pieces `oi" each set being directed toward each other and the pole faces thereof being arranged in spaced-apart relation in order to receive therebetween the opposite ends of a pivotally mounted armature formed of magnetic material.

Preferably, the winding spool and armature assembly 2| is of the construction of that disclosed and claimed in the copending application of Albert E. Woodruff, Serial No. 209,803, filed May 24, 1938, and as shown in Figs. 5 and 6, comprises a winding spool 33 formed of insulating material such as Bakelite and an arma.- ture 34 formed of fiat magnetic stock. Preferably the armature 34 is formed of steel containing approximately 4% silicon and has an A. C. permeability of the order of 500 to 1500.

The Winding spool 33 is split longitudinally and comprises complementary Vupper and lower sections 33a and 33h, respectively, of similar construction. Each of the sections includes a body 35 carrying two spacedapart winding retaining heads 36'. The wall of the body 35 of the lower section 33b is provided with a longitudinally extending recess 35a therein, which is disposed adjacent the joint between the upper and lower sections 33HL and 33D, respectively. The wall of the body of the upper section 33EL is substantially fiat adjacent the joint between the upper and lower section 33a and 33h, respectively. The armature 34 is provided with a longitudinally extending operating lug 34a and two transversely extending spaced apart lugs 31 intermediate the ends thereof. Each of the lugs 31- projects` from one side of the armature 34 and is provided with a head 31 connected yby a length 3'!b to the armature 34, the-length 3`|b being of reduced cross-sectional area.A The armature 34 is arranged in the recess asa provided in the wail of the body as of the lower section 33h, the armature 3i being retained in position by spaced apart and aligned recesses 35h provided in the body 35 of the lower section 33h and receiving the heads 312l onthe lugs 31. The lugs 31 are retained in the recesses 35b provided in the body `35 ofthe lower section 33br by two mounting clips 38. Eachof the clips 38 is of substantially U-shape, comprising two flanges 33 and 4B, the flange 40 beingprovided with three the lugs 31, thereby rigidly securing the lug to the body 35 of the lower section 33h. 'I'he clips Samount the armature 3d on thebody 35 of the lower section 33b for vibratory movements about an axis extending between the lugs 31 transversely of the winding spool 33.

In constructing the assembly 2! the armature 3d is brought into position with respect to the recess 35e provided in the body 35 of the preformed lower section 331 of the winding spool 33 and lowered into place, the heads 31e on the lugs 31 being received in the recesses 35h formed :in the .body 35. The clips 38 are then placed upon the sides of the body 35 and the outside fingers liti and #itc and. the flange 33 are bent into engagement with the body 35 in order securely to fasten the clips 3S thereto. The armature 3d is then aligned and the intermediate fingers dei are then bent into engagement with the heads 31a on the lugs t1, in order securely to retain the armature 31i in position. The pre-formed upper section 33B is then brought into superim-x posed relation with the lower section 33h to complete the assembly 2i, the upper and lower sections 338 and 33h, respectively, being retained together by the iield structure of the telephone transmitter in any suitable manner.

, bei 23h to the diaphragm se.

The walls of the bodies 35 of the upper and` lower sections 33a and 33h are spaced a short distance from the armature 3ft and the ends o the armature 3d project through the winding spool 33, these ends of the armature being protected against injury by projections e2 provided on the ends of the sections 33a and 33h. Thus, the composite body of the winding spool 33 is hollow; and is provided with a wall surrounding a narrow opening extending longitudinally therethrough, the armature 3d being arranged within the opening in the body. The armature 3d is supported by the lugs 3i for vibratory movements out of contact with the wall of the .body and about an axis extending between the lugs 31 transversely of the winding spool 33. When the armature 33 is moved from its normal position, the lugs 31 are subjected to torsional strains, these strains being localized in the lengths of cross-sectional area 31h of the lugs 31. This torsional Amounting of the armature 3ft is very advantageous as it causes the amature Mto be deflected an amount precisely corresponding to the force exerted on the operating lug 3d, the deection of' the armature 3d beingdirectly proportioned to the force exerted upon the operating lug 34a overa wide range.4

A winding 43 is arranged-about the body be, tween the winding retaining heads 3B of the winding spool 33 and one end 33h of the armature 3ft is disposed between the oppositely disposed pole faces of the set of adjacent pole pieces i opening Q9 3i and 32, while the other end 36 of the armature 3d is disposed between the oppositely disposed pole faces of the set of adjacent pole pieces 29 and 30. The operating lug 33a on the armature 3d is provided with an opening therein in which one end of a rod 44 is secured, the rod et extending through an opening t5, formed in the field member 23a. The other end of the rod ad is secured to a sound wave responsive diaphragm d6 supported about its periphery by suitable clamping means d1. Also, an opening d@ is provided in the iield member 23b in case it is de sirable to extend the rod 6d through the mem- This arrangement provides for extending the rod @d through either one of the eld members 23 or 23D, thereby rendering reversible the position of the diaphragm l5 with respect tothe eld structure dil.

Normally, the armature 33 occupies a position wherein the opposite ends thereof are disposed intermediate the adjacent pole faces of the two sets of. pole pieces and is adapted to be vibrated by the rod id when the diaphragm e@ is vibrated by sound waves impinging thereon. Thus, the movement of the armature 3d is controlledin accordance with the vibratory movements of the diaphragm d3, the vibratory movements of the diaphragm :te corresponding to the vibrations oi the air produced by the sound to be transmitted. As the armature 3d is moved in a clockwise direction about its pivot, the magnetic field of the field structure Ztl traverses a path extending from the north pole of the bar magnet 22 by way of the iield member 23a, the pole piece 3i, the armature 3d, the pole piece 322 andthe iield member 23h to the south pole of the bar magnet 22. On the other hand, when the armature is moved in a counter clocirwise directionabout its pivot, the magnetic field of the iield structure 2E traverses a path ex tending from the north pole of the bar magnet 22 by way of the field member 23a, the pole piece ES, the armature 3d, the pole piece 32 and the field member 33h to the south pole of the bar mag= net Z2. Thus, during the vibratory movements of the armature Sli the magnetic iield of'the eld structure 2i? traverses the armature Sli in op posite directions, causing a corresponding electrornotive force to be generated in the winding t3 electromagnetically coupled thereto The electrornotive force generated in the winding it is transmitted to a distant point where it is utilized in a suitable receiver or other translating device to reproduce the sound transmittedin a wellknown manner. l

The pole faces of. the two sets of pole pieces are secured together in spaced-apart relation by an arrangement including two spacing elements QS, shown in Figs. 7 and 8, formed of nonmagnetic material, and arranged between the body portions of the field members 23a and 23h. Preferably, each of the spacing elements 3S is formed of Bakelite and is provided with an extending longitudinally therethrough and arranged in alignment with. two openings Sil and 5I ,formed in the eld members 23E- and 23h, respectively. Each of the spacing elements Il@ is secured in place by a stud 'or securing element 52 formed of non-magnetic material extending through the aligned openings 53, I9 and 5i, and threaded finto an opening provided in a supporting plate 53. Preferably, each o the studs 52 is formed of brass and is surp rounded by a resilient washer 5d disposed between oppositely extending teeth 54a engaging the iield member 23a -and the spacing element 49l This.

arrangement compensates for the dierence in the thermal coeicients of expansion of the studs 52 and the spacing elements 49, and retains the iield members 23a and 23b securely together in spaced-apart relation in spite of variations in the ambient temperature. Also, each of the spacing elements 49 is provided with a fiat surface 49b abutting the winding retaining heads 36 of the winding spool 33, the spacing elements being disposed adjacent the opposite sides of the winding spooland armature assembly 2| thereby to retain the assembly in place. A recess 55 is provided in each of the spacing elements 49 in order to accommodate the conductors extending electrical connections to the winding 43.

In assembling the sound translating device the extreme outer ends of the bar magnet 22 are inserted in the recesses provided in the iield members 23'a and 23b by the apertures 25a formed in the inside elements 25 thereof. The bar magnet 22 and the leld members 23a and 23b are then securely fastened together by a stud or the like extending through the recess 26 formed in the bar magnet 22 and the aligned openings v2`| and 28 formed in the iield members 23a and 23", respectively. The previously assembled winding spool and armature assembly 2| is then slid into place between the two sets "of pole pieces and connections are extended to the terminals of the winding 43. The spacing elements 49 are then arranged between the body portions of, the field members 23a and 23b1and secured in place by the studs 52. Finally, the rod 44 is inserted through the opening 45 formed in the iield member 23a and the opposite ends-thereof are connected to the operating lug 34a formed on the armature 34 and the diaphragm 46. I

In a modiiied form of the field structure two field members 60 of similar construction are secured in face engagement with the-opposite ends of the bar magnet 22. Each of the iield members, as best shown in Figs. 9 and 10, is formed of flat magnetic stock and provided with an extended body portion having two pole pieces 6| and 62 spaced from each other, the pole pieces and 62 being formed integrally with the stock of the field member 60. The two pole pieces on each of the field members cooperate with each other to provide two sets, the pole pieces of each set being directed toward each other and the pole faces of each set of pole pieces being arranged in spaced- "apart relation. The iield members 60 are assembled upon the opposite ends of the bar magnet 22, and the windingspool and armature assembly 2| is arranged betweenl the two sets of pole pieces in an obvious manner. The construction and operation of this form of the field structure is otherwise the same as the form of iield structure illustrated in the sound translating device of Fig. 1.

From the foregoing description it is apparent that a compact and rugged sound translating device is provided. Moreover, soundy translating devices of this construction have high operating utilizing the combination of a permanent magnet having high maximum energy characteristic, pole pieces having a high A. C. permeability and a vibratory armature having a high A. C. permeability. Als'o the efficiency of the device is maintained at its maximum value by forming the permanent magnet of a material having high coercivity. While the'features of the present invention have been illustrated as being embodied in a telephone'transmittenit is apparent thatl they may be readily embodied in a telephone receiver or other sound translating device.

While there have been described what are at present -considered to be the preferred embodiments of the invention, it will be understood that various modifications may be made therein and it is contemplated to cover in the appended claims all such modiiications as fall within the true spirit and scope of the present invention.

What is claimed is:

1. A sound translating device comprising, in combination, a bar magnet, iield members formed of magnetic material arranged on the opposite ends of said bar magnet, said field members having longitudinally extending body portions carrying two pole pieces spaced from each other and constituting two sets, the pole pieces of each of said sets being directed toward each other and the pole faces of each set being arranged in spaced-apart relation in order to receive therebetween the opposite ends of an armature mounted for pivotal movement about a laterally extending axis, a winding spool arranged between said two sets of pole pieces, two laterally spacedapart spacing elements formed of non-magnetic material arranged between the body portions of said iield members, said spacing elements being disposed exteriorly of said winding spool and adjacent the opposite sides thereof, and means including a securing element and said spacing elements for securing said field members together in spaced-apart relation and for preventing movement of said winding spool between said two sets of pole pieces in a lateral direction.

2. A sound translating device comprising, in combination, a bar magnet, iield members formed of magnetic material arranged on the opposite ends of said bar magnet, said field members havof said sets being directed toward each other and efficiencies, it being possible t0 produce between the pole faces of eachset being arranged in vspaced-apart relation in order to receive therebetween vthe opposite ends of an armature mounted for pivotal movement about a laterally extending axis, -a winding spool arranged between said two sets of pole pieces, two laterally spaced-apart spacing elements formed of nonmagnetio material extending between the body portions of said iield members, said spacing elements being disposed exteriorly of said winding spool and adjacent the opposite sides thereof, and means including two securing elements extending between the body portions of saiddiield members and said spacing elements for retaining said viield members together in spaced-apart relation and for' preventing movement of said winding spool between said two'sets of pole pieces in a lateral direction in place, and means including resilient washers interposed between one of said iield members and said spacing elements for com-y pensating for the diierence in the thermal coeiiicients of expansion of said securing elements and said spacing elements.

- arranged 3. A sound translating device comprising, in

combination, a bar magnet, field members formed of magnetic material arranged on the opposite ends ofjsaid bar magnet, said field members having longitudinally extending body portions carrying two pole pieces spaced from each other a'nd constituting twosets, the pole pieces of each f of said sets being directed toward each other and the pole faces of each set being arranged in cluding a securing element and said spacing ele- -ments for securing-said field members together.

in spaced-apart relation and `for preventing movement of said winding spool between said two sets of pole pieces in' a lateral direction.-

4. A sound translating` device comprising, in combination, a bar magnet, field members formed of magnetic material arranged on the oppositel ends of said bar magnet, said eld members having recesses therein receiving and surrounding the extreme outer ends of said lbar magnet, thereby to minimize flux leakage betweenthe ends of said bar magnet, said field members having outwardly extending body portions carrying -two pole pieces spaced from each other and constituting two sets, the pole pieces of each of said sets being directed toward each other and the pole faces of each set being arranged in spaced-apart relation in order to receive therebetween the opposite ends of a pivotally mounted armature, a winding spool arranged between said two sets of pole pieces, two spacing elements formed of non-'magnetic material arranged between the body 'portions of said field members and disposed adjacent the opposite sides of said winding spool, and means includinga securing element and said spacing elements for securing said field members together in spaced-apart relation and for retaining said Winding spool in place. l

5. A sound translating device comprising', in combination, a bar magnet, similar field members formed of magnetic material arranged on the opfposite ends of said bar magnet, each of said eld members including inside and outside elements formed of fiat stock and secured togetherin facing engagement, each of said inside elements having an aperture therethrough in alignment with a solid portion of the outside element secured thereto, thereby providing a recess in each of said field members, the recesses in said field members receiving and surrounding the extreme outer ends of said bar magnet. thereby to minimize flux leakage between the ends of said bar magnet, a pole piece formed integral with each of said inside and outside elements. the pole pieces formed integral with corresponding elements being directed toward each other and constituting a set, said sets of pole pieces being spaced from each other `and the pole faces of each set being arranged in spaced-apart relation, a winding spool arranged between said two sets of pole pieces, said winding spool having an armature pivotally mounted thereon, the opposite ends of said armature being arranged between the pole faces of the pole pieces l 5 of said two sets, two spacing elements formedof non-magnetic material arranged between the body portions of said field members and disposed adjacent the opposite sides of said winding sp'ool, and means including a'securing element and said 'spacing'elements for securing said field members.

togetherin spaced-apart relation and for retaining said winding spool in place.

6. A field structure for a sound translating device comprising, in combination, a bar magnet, field members formed of magneticA material arranged on the opposite ends of said bar magnet. at least one of said field members including in- V side and outside elements formed of flat stock and secured togetherin facing engagement, said inside element having an aperture therethrough in alignment with a solid portion of said outside element, thereby providing a 4recess in said one field member, the recess in said one field member receiving and surrounding one extreme outer end of said bar magnet, thereby to minimize flux leakage from the one end of said bar magnet', and a polepiece carried by each of said field members, said pole pieces being directed toward each other and constituting a set, the. pole faces of said set of pole pieces being arranged in spaced-apart relation in order to receive therebetween a movable armature. v

7. A field structure for a sound translatingdevice comprising, in combination, a bar magnet,

. similar eld members. formedof magnetic material arranged on the opposite ends of said bar f magnet, each of said field members including inside and outside elements formed of flat stock and secured together in facing engagement, each a setthe pole faces of said set of pole pieces being arranged in spaced-apart relation in order to receive therebetween a movable armature.

8. A field structure for a sound translating device comprising, in combination, a bar magnet,`

similar field members formed of magnetic mal terial arranged on the opposite ends of said bar other and constituting a set, said sets of pole magnet, each of said field members including inside and outside elements formed of fiat stock and secured together in facing engagement, each of said inside elements having an aperture therethrough in alignment with a solid portion of the outside element secured thereto, thereby provid' ing an recess in each of said field members, the recesses in said field members receiving and surrounding the extreme outer ends of said bar magnet. thereby to minimize flux leakage between the ends of said bar magnet. and a pole piece formed integral with each of said inside and outside elements, the pole pieces formed integral with corresponding elements being directed toward each nieces beine spaced from each other and the pole faces of each set being arranged in spaced-apart relation in order to receive therebetween the opposite endsof a pivotally mounted armature.

9. A -sound translating device comprising, in combination, a bar magnet, similar field members formed of fiat, magnetic` stock arranged on the opposite ends of said bar magnet, said field members having outwardly extending body portions provided 4.with two pole pieces spaced from each other and constituting two sets, the' two pole p ieces provided -on each iield member .being formed integral therewith from the stock of said `iield member, the pole pieces of each of said sets faces of each set being arranged in spaced-apart relation, a winding spool arranged between said twosets of pole pieces. said winding spool having being directed` toward each other and the pole faces of each set being arrangedin spaced-apart 1 relation in order to receive therebetween the opposite ends of a pivotally mounted armature, a winding spool arranged between said two sets of pole pieces, two spacing elements formed of nonmagnetic material arranged between rthe body portions oi' said eld members and disposed adjacent the opposite vsides of said winding spool,

and meansincluding a securing element and said spacing elements for securing-said ileld'members together in spaced-apart relation and for rei taining said winding spool in place.

. 10. A sound translating device comprising, in combination, a bar magnet, similar fleld members formed of fiat magnetic stock arranged on the opposite ends of said bar magnet, said eld members having outwardly extending body portions 'provided with two pole pieces spaced from each other and constituting two sets, the two pole 'pieces provided on each ileld member being formed integral therewith from the stock oi said fleld member, the pole pieces of each of said sets being directed toward each other and the pole an armature pivotally mountedthereon, the opposite ends of said armature being arranged be.-

tween ythe pole faces of the pole pieces of said two sets,` two spacing elements formed of non- Amagnetic material arranged between the-` body portions of said eld members and disposed adjacent the opposite sides of said winding spool, A and means including a securing element and said spacing elements for securing said eld meml bers together in spaced-apart relation and for retaining said winding spool in place.

11. A sound translating device comprising, combination, a bar magnet, a pair of ileld members secured in spaced-apart relationship, each of said eld members including inside and outside plates secured together in facing engagement, said inside plates having aligned openings therethrough in alignment with solid portions of said 

